1. Field of the Invention
This invention relates generally to fasteners and, more specifically to locknuts adapted for use with threaded shafts, such as bolts.
2. Discussion of the Related Art
Nuts are commonly provided with an inner thread that is adapted to engage an outer thread on a shaft. Rotation of the nut relative to the shaft moves the nut axially along the shaft. The threads of the nut can be tightened on the threads of the shaft by applying a torque, the magnitude of which depends on the resistance to rotational and axial movement. This torque places stress on the inner threads of the nut, the outer threads of the shaft, the shaft itself, and any object resisting axial movement of the nut relative to the shaft. Any one of these elements of structure can fail when the torque exceeds a particular value. Accordingly, it is often desirable to limit the torque that can be applied to the nut in order to inhibit failure of these various structural elements. One element that is commonly overstressed is the shaft, particularly when it is provided with a tubular configuration. Under these circumstances, the walls of the shaft are particularly susceptible to breaking under high torque conditions. The structure of the shaft is even further susceptible to breakage when the shaft is made of a non-metal material such as plastic.
In the past, torque-limiting nuts have been provided but typically with very complex structures involving many parts, and a tedious manufacturing process. These nuts have also commonly been made of metal, which does not benefit from the injection molding techniques available to plastic materials. The nuts have also been provided with designs that tend to fail at the torque limit rendering them subsequently useless. In some cases, the nuts have desirably provided a limiting torque in the forward direction, but have undesirably also provided that limiting torque in a reverse direction. Often this has made it impossible to remove the nut.